Recently, in the field of display devices, there are demands for advanced technologies such as smaller thickness, lighter weight, larger area, various arbitrary shapes and curved display.
Especially, as for display devices used in portable apparatuses, there are strong demands for lighter weight and long durability. As use of portable apparatuses expands, display panels using plastic substrate in place of glass substrate have been studied and put into practical use in some cases.
However, as the display shifts to color movies, there are growing demands for higher-speed response of display device and for TFT (Thin Film Transistor) display devices, organic EL (ectroluminescence) devices and the like. Glass substrates are still being employed as substrates for these display devices and it is hoped to shift to plastic substrates reduced in weight and excellent in durability.
However, heat resistance of conventional plastic substrates is insufficient, which may cause warpage or deformation in the step of forming metal semiconductors or insulating films through CVD (Chemical Vapor Deposition).
Further, since the difference in the thermal expansion rate between resin layer constituting the substrate and the electrode is large, cracking tends to generate especially in the transparent substrate of TFT liquid crystal substrate which is exposed to drastic temperature change at the time of processing, which may result in increase in electric resistance value or sometimes in disconnection, and therefore practical application of such substrates has not begun yet.
Although some types of heat-curable resins such as epoxy resin have an improved heat resistance, transparency of such types of resin is insufficient. In contrast, those having good transparency have a low glass transition temperature (Tg) and are inferior in heat resistance.
Liquid crystal display devices can be categorized into transmissive type liquid crystal, reflective type liquid crystal and semitransmissive type liquid crystal as a mixed type of reflective type and transmissive type.
A transmissive type liquid crystal display device is a type of device displaying images by using backlight at the back surface of the display screen as light source, having high chroma saturation, which can realize eye-friendly screen even in a dark room. But it has a disadvantage that a measurable amount of power is required.
On the other hand, a reflective type liquid crystal display device is a type of display device, using reflection of outside light to display images, has been attracting attention for its battery-friendliness, and attempts to make the substrate plastic have been made. For example, Japanese Patent Application Laid-Open No. 11-2812 shows that a laminate plate comprising fiber cloth impregnated with resin or the like, such as glass epoxy laminate, is used as substrate for a reflective liquid crystal display device. However, reflective conductive substrate shown there, which uses white pigment in the reflective layer, cannot meet the recent demand for high precision and high contrast display.